I. Field of the Invention
The present invention relates to a device for the reduction of heat losses due to flue gases in boilers which are operated with oil or gas.
II. Description of the Prior Art
When oil or gas is burned in a boiler, water vapor will result due to the hydrogen with water which was contained in the fuel. This water vapor precipitates from the flue gas if the temperature falls to a temperature below the due point. In case of the sulfur containing heating oils which are preferably used for the operation of boilers, the due point is located at approximately 150.degree. C. The boiler and the burner must therefore be constructed and operated in such a way that the temperature of the flue gases does not fall below the due point temperature in any part of the installation; that is, up to the end of the smokestack. In order to have available at the end of the smokestack a flue gas temperature of at least 150.degree. C., the flue gas temperature at the end of the boiler is approximately 210.degree. C. to 270.degree. C. If the boiler is operated in such a way that the high heat capacity of the flue gas is not taken advantage of, heat losses of various types result which can amount to 20 % to 30%, depending upon the construction of the boiler, in comparison to a heating installation where the flue gas would leave the boiler at a temperature of approximately 20.degree. C. The resulting heat loss is a combination of the flue gas loss which exists due to the high temperature of the flue gases. Another heat loss results because of unburned carbon monoxide. This loss can, of course, be prevented if an amount of air is available which is sufficient for the complete combustion of the carbon monoxide. However, since in this case the flue gas losses are substantially increased, a loss of carbon monoxide in the amount of 0.5% to 1.5% must be considered tolerable. Another source of losses is due to the fact that the heat of condensation of the water vapor that is contained in the flue gas is not taken advantage of in order to reduce these heat losses. Heat losses may be reduced by a heat exchanger located behind the boiler, for instance, in the form of tubes through which heating water is passed and subsequently returned to the boiler. This heat exchanger removes heat from the flue gas, which heat is used for the preheating of the heating water with the result that the flue gases in the area of the heat exchanger are cooled; and, thus, the heating water in the heat exchanger is heated corresponding to the degree of cooling. If a corrosion-resistant heat exchanger is used, a temperature below the due point temperature of 150.degree. C. can actually be reached when the flue gases are cooled. In this case the water vapor which has condensed and formed liquid water precipitates at the heat exchanger and the precipitated water is collected, neutralized and removed after it has been further cooled. If the return temperature of the heating water through the boiler is 60.degree. C., the temperature of the flue gases could be reduced to approximately 70.degree. C., in which case the dew point temperature also is 70.degree. C. In this case the flue gases behind the heat exchanger are present in the form of 100% saturation such that for any further cooling a further precipitation of condensed water will result; however, since the flue gases after leaving the heat exchanger and on their way into the free environment are necessarily subjected to further cooling, a cooling of the flue gases to 70.degree. C. can actually not be achieved by using a heat exchanger, but rather the flue gas which leaves the heat exchanger must exhibit a temperature which exceeds the dew point of 150.degree. C. to such an extent that a precipitation of condensed water is prevented up to the end of the smokestack. Therefore, the flue gas temperature can actually not be reduced to the optimal value of 70.degree. C. by means of the heat exchanger when the hot water temperature is 60.degree. C., but rather cooling can only be achieved up to a correspondingly higher temperature, such as 200.degree. C., in order to prevent a precipitation of condensed water after leaving the heat exchanger.
III. Prior Art Statement
In the opinion of the applicant, the aforementioned description represents the most pertinent prior art of which applicant is aware.